The present invention relates to the automotive timing chain art. The preferred embodiments of the invention find particular application in conjunction with a chain tensioner device for use in confined spaces that applies a tensioning force to a drive chain traveling therepast, and will be described with particular reference thereto.
Chain guides and various mechanical tensioning devices are used in many internal combustion engine timing chain drive applications. With reference to FIG. 1, a conventional chain drive system 10 rotates in a clockwise direction as shown by arrow 11. The chain drive system 10 includes at least a drive sprocket 12, a driven sprocket 14, and a chain 16 (e.g. roller chain, inverted tooth chain, etc.) having a number of chain links 18. As known in the art, the chain drive system 10 can include additional sprockets such as idler sprockets, balance shaft sprockets, etc.
The chain 16 engages and wraps about sprockets 12 and 14 and has two spans extending between the sprockets, slack strand 20 and taut strand 22. A central portion of the taut strand 22 may be guided between the driven sprocket 14 and the drive sprocket 12 with a conventional chain guide (not shown). The taut strand 22 of chain 16 is under tension as shown by arrows 26.
A conventional blade-type mechanical tensioner assembly 24 applies a tensioning force to the slack strand 20. The tensioner assembly 24 includes a bracket 28, typically formed by stamping as a rigid metal bracket, and an elongate shoe sub-assembly 30. The bracket 28 includes a pin 32, typically resistance welded to the bracket at a pivot end thereof, to provide for shoe support and rotation capability. The bracket 28 also includes a ramp 33, acting as a bearing surface, at the opposite or bracket free end to provide for the required shoe translation as well as reaction support.
The shoe sub-assembly 30 includes a chain-engaging shoe member 34, and a blade spring 36 that provides the shoe sub-assembly 30 with the resiliency and rigidity that is necessary to apply the proper amount of tensioning force to the slack strand 20. The tensioning shoe or blade 34 is typically molded using a heat-stabilized nylon. The blade spring 36 is typically formed from spring steel, and is mechanically interlocked to the shoe.
The tensioner design, as well as the method and order of installing the tensioner to an automotive engine, is normally determined by the packaging parameters. Fastener location, an integral part of the packaging parameters, is always an important design issue. For instance, the packaging parameters of the drive 10 permit and/or require that a first fastener 40a be located outside a path of expected chain travel, and a second fastener 40b be located inside the path of expected chain travel. Both fasteners 40a, 40b clamp the bracket 28 to an engine case or block. The bracket 28 is positioned to properly orient the chain-engaging shoe member 34 with respect to the slack strand 20 that is located between the fasteners 40a, 40b. 
The use of a stamped metal bracket is a reasonable design approach when the fasteners can be positioned at a desired location, and have a desired separating distance, while at the same time not interfering with a preferred pivot location or a preferred free end ramp location. A disadvantage of the prior art tensioner 24 is that the free end ramp 33 of the stamped metal bracket 28 does not permit a fastener (e.g. 40a, 40b) to be located either below or close to the reaction surface of the ramp.
That is, the ramp 33 is formed by stamping the metal bracket so that an edge thereof is angled substantially perpendicular (orthogonal when viewed in FIG. 1) to the remainder of the bracket. The tab 33a is then bent substantially perpendicular to the ramp 33 so that the tab 33a extends substantially parallel with the remainder of the bracket. Thus, there is no bracket material proximate the tab 33a with which to provide an aperture for a fastener. The fastener locations must necessarily be placed on the remainder of the bracket that was not bent to form the ramp 33 and the tab 33a. This can be a problem when a preferred fastening location is in fact below or in close proximity to the ramp.
Accordingly, it is considered desirable to provide a new and improved a chain tensioner device that meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.
The principal object of the present invention is to provide a mechanical tensioner assembly that can package in confined spaces, primarily for automotive engine chain drives.
In accordance with one aspect of the present invention, a chain tensioner is provided. The chain tensioner includes a bracket and a shoe sub-assembly pivotally secured to the bracket, wherein the shoe sub-assembly is formed from a plastic material and the bracket is formed from a plastic material with a filler material added thereto.
In accordance with another aspect of the present invention, a method of assembling a chain tensioner having a bracket and a shoe sub-assembly is disclosed. The shoe sub-assembly is formed from a plastic material and the bracket formed from a plastic material with a filler material added thereto. The bracket includes a recess, an aperture, and a raised hub surrounding the aperture. The shoe sub-assembly includes a blade locking tab and a tab portion having a tab aperture with a counterbored portion. The method includes the steps of joining the shoe sub-assembly to the bracket such that the raised hub is positioned within the counterbored aperture portion; rotating the shoe sub-assembly relative to the bracket to position the blade locking tab within the recess; and inserting a removable installation ring through the blade locking tab and the recess to lock the shoe sub-assembly to the bracket to provide a one-piece tensioner assembly.
The present invention utilizes a synthetic plastic (e.g. nylon) bracket that permits a fastener at a pivot end of the bracket to serve as a pivot pin for a shoe sub-assembly as well as a bracket fastener. It also allows for greater flexibility for the fastener location at a free end of the bracket. A preferred and more robust nylon bracket design permits the free end fastener to be positioned very close to, or substantially below, a reaction surface of the bracket. The nylon bracket serves to reduce the weight of the tensioner assembly. Another advantage is that the nylon bracket is more cost-effective than a metal bracket. Further, the nylon bracket beneficially decreases the transmission of noise and vibration compared to a steel bracket, thereby enhancing NVH characteristics of the drive.
The present invention beneficially utilizes an interlocking feature at the pivot end, which serves to advantageously maintain an interlock of the shoe-to-bracket in cooperation with an installation pin. Additionally, a xe2x80x9cpositioning featurexe2x80x9d is disclosed in a bracket mounting hole. The positioning feature is used at the pivot end of the bracket. In order to permit the free rotation of the shoe, the pivot end of the bracket is necessarily not clamped rigidly to the engine case when a pivot end bolt is installed. Further, the utilization of a cost-effective dowel pin at the pivot end of the bracket is also disclosed.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment.